An interactive whiteboard usually is a board with a size from 32 inches to 144 inches for user interaction, so the package of an interactive whiteboard is very bulky and heavy for shipment. An interactive whiteboard system comprises a whiteboard and interactive whiteboard modules. Making the interactive whiteboard system portable requires that the interactive whiteboard modules are of small size and light weight when packed during shipping. In the art, it is achievable by not limited to a large physical board. A flat surface such as an ordinary whiteboard, a wall, a glass window, a table, etc. may be selected to act as a board as well. A projector is used to project a content image on the flat surface. A touch action by an object on the flat surface is sensed by a sensing unit to find out a touch point's coordinate, which is used to update the content image so that interaction with a user is achieved. Such approach is adopted in the disclosures of US2013/0070089 and US2013/0141389. In US2013/0070089, the sensing unit has two image sensors fixed and aligned by a control device. This sensing unit is made bulky and heavy due to the presence of the control device. In US2013/0141389, the sensing unit comprises two camera devices connected by a chord for ensuring that the two camera devices are on the same plane. The presence of the chord makes the sensing unit difficult to be packed up in a small size.
There is a need for an interactive whiteboard module or a sensing unit comprising such module such that an interactive whiteboard system based on such module or unit results in a small size when packed.